Overhead Line Wood Pole Assessment

How Our Assessment Works

Three 10 mm diameter holes, equally spaced around the pole circumference, are drilled at ground line and angled downwards at 45°, targeting the critical zone approximately 100 mm below ground level.

A Shell Depth Indicator is then inserted to accurately measure the depth of sound wood and any internal decay. Evidence from North America – where over 200 million poles are routinely assessed using drill-and-test programmes – shows that this method results in only a 2-3% reduction in pole strength, depending on pole size. These same holes can later be used to inject rot-prevention paste and to recheck for changes during future inspections. Each pole is also visually assessed for pockets of decay, external damage, woodpecker activity, and pole-top rot.

All gathered data – together with information such as line loading, conductor type, span length, angle or line deviation, and stay configuration – is entered into a handheld device running specialist software. This calculates the RSV of the pole and determines its “fitness for purpose” against the original overhead line design parameters and safety factors.

If a pole fails at ground line, cost-effective reinforcement can extend its service life by up to 20 years. EP Marine & Rail provides recommendations for reinforcement or rot treatment to extend service life.

Scientific & Operational Benefits

• Objective, Quantifiable Results: Specialist software calculates true remaining strength based on measured data – not visual estimates.

• Preserves Infrastructure: Saves over 60% of S poles and 30% of D poles, reducing unnecessary replacements.

• Reliable, Repeatable, Auditable: Each test generates digital records for long-term traceability and compliance.

• Proven Safety Margin: Results are benchmarked against the original design factor of safety, ensuring network reliability.

• Remedial Insights: Detects decay early, enabling timely treatment and preventing costly failures.

• Cost-Effective Asset Management: Fewer replacements mean less disruption, hence reduced CMLs and CIs, and longer asset life.

Why Our Approach Outperforms Traditional Methods

Traditional Methods

Resistograph / Microprobe Drill

Originally designed for arboriculture (testing a few trees per day), this method is poorly suited to large-scale pole assessment – typically 50 poles per day, requiring around 150 holes. The small 3 mm drill bit follows the line of least resistance when encountering voids or fissures, often giving false readings. Frequent bit breakage, high maintenance costs, and unreliable data make this an inefficient and inconsistent process for utility use.

PURL – Pole Ultrasonic Rot Locator

This method uses transducers placed on opposite sides of the pole at or near ground level to detect air pockets using ultrasonics. However, unless soil is excavated around the pole, adding considerably to cost, so transducers can be positioned below ground line (where over 90% of decay occurs), the results are of limited value. If the pole is wet, readings become even more inconsistent.

Single Drill Method

A single 10 mm hole is drilled around 1 m above ground, meaning the critical ground-line area is not inspected. This technique is typically used only to check suitability for reinforcement, not to assess true structural fitness or remaining strength.

Traditional inspection techniques such as Resistograph drilling, PURL ultrasonic testing, and single-hole assessments all have inherent limitations. They often fail to assess the critical ground-line zone, where the majority of decay occurs, or rely on small, fragile drills that produce unreliable readings. Many of these methods are disruptive, time-consuming, and deliver inconsistent data that cannot be verified or modelled digitally.

The EP Marine & Rail Method

At EP Marine & Rail, we take a fundamentally different approach. Our wood pole assessment method combines targeted ground-line drilling, precise shell-depth measurement, and precision software analysis to deliver an accurate, science-based understanding of each pole’s structural integrity. The result is a quantifiable RSV which shows if the pole is fit for service according to its original design, strength and factor of safety.

Because we measure the pole’s actual geometry and decay profile, not just surface condition or arbitrary shell thickness, our method provides a complete picture of pole health. Data is captured digitally and modelled in real time, producing auditable, repeatable, and objective results that stand up to engineering and regulatory scrutiny.

This approach not only improves accuracy and safety, but also extends life and reduces unnecessary replacement with up to 60% of S poles and 30% of D poles reclassified as serviceable. Minimal disruption, clear data, and proven reliability make our process the most effective and cost-efficient way to manage pole networks sustainably keeping CMLs and CIs to an absolute minimum.

Our Commitment to Network Safety and Longevity

Our wood pole assessment protocols are built on decades of international research and field validation. Evidence from North America and Europe demonstrates that modern, non-destructive testing programmes, supported by specialist software, deliver the most effective balance between safety and asset longevity.

By combining scientifically proven methods with our team’s practical expertise, EP Marine & Rail helps DNOs maximize asset life, improve inspection accuracy, enhance network resilience, reduce CMLs and CIs – all while maintaining the highest safety standards.

90% of all rot occurs at ground line to 100 mm below